Warhol's 15 minutes of fame limit automatically limits the number of "everyone" and "fame" quite considerably
In the future, everyone will be world-famous for 15 minutes.
In a normal human's life of 80 years there are 2803200 quarter hours, make that a round 3 million. So the future will have at most 3 million humans. And those will be surprisingly busy considering that current humans get to meet about 10000 other people throughout their live and typically remember the names of only a few hundreds.
Current humans also sleep and spend some time for themselves - Activities that are already sadly undervalued in present.
Mulling the thought for an hour, 15 minutes to write, 1 minute to read. Time is funny.